I need to find a solution to the P0505 code too. I cleaned my IACV earlier this year and it was clean as a whistle. Put it back on, not too long after, P0505 code. Not too long after that, I started getting all sorts of idle problems and got multiple codes. Something about the foot pedal, another catalyst malfunction bank 1 or something code, codes just started popping out of no where. But every time I used an OBDII scanner to clear the codes, car is fine for a few weeks. And when the CEL comes on, about 30 minutes after they're on, car drives fine, no idle problems at all. Every once in a while the car will bog at 1500 when I lightly hold the gas and when I'm driving in gear and let off the gas, the car jerks real hard and jerks hard again when I hit the gas. So I turn off the car, turn it right back on, and it drives perfectly fine again. Idle goes back down to 7-900 where I set it before. It's mind boggling.
I checked for vacuum leaks but I don't have any. I tried unplugging the IACV and it does nothing, but the second I plug it back in, the idle starts bouncing between 1100 and 1500. So I turn off the car, turn it back on, and it's normal again. I don't really have money right now to get another IACV.